This results in 14C incorporation in all newborn cells with a “time stamp” assessed

by known decreasing atmospheric 14C concentration since that time. Though they find clear evidence of ongoing cell birth in the OBs of these select adult humans, this is found to be almost all nonneuronal, using broad neuronal versus non-neuronal marker combinations for sorting of nuclei for 14C analysis. These results are rigorously based and the experiments solidly performed. But is the question put to rest? Though these data are very intriguing and certainly weigh in Y-27632 concentration on how generally dependent adult humans are on olfactory bulb neurogenesis in affluent, Western cultural settings (seemingly not much at all), there are caveats and limitations to consider before making strong conclusions about the existence of adult neurogenesis in the human olfactory bulb. One main caveat concerns the approach itself, which is

not able to identify new neuron birth in which the adult-born neurons go on to die. Results in mice (Magavi et al., 2005 and Lazarini and Lledo, 2011) have shown that adult-born neurons not activated by novel odorants Selleck Navitoclax while they are forming synaptic circuitry in the OB go on to die. Further, results in rodents have found that adult-born neurons do not serve as simple “replacement parts” for developmentally born neurons but rather serve as part of a unique function of novel odorant learning. Thus, some of the basic assumptions used in the current work about the relative percentages of 14C-labeled OB neurons might be incorrect; there might be a higher percentage turnover in a smaller subset below of adult-born neurons—but only if novel odors are often

encountered. What these data might actually confirm is that average humans in some affluent and Western societies are not nearly as olfaction-dependent as our hunter-gatherer ancestors or as modern humans in cultures with more novel odors day-to-day (smellier environments, frankly) or as those among us who are chefs, sommeliers, perfumers, vintners, “foodies,” nomads, back-country hunters, or multicultural travelers or migrants. The question remains. The detailed lists of human subjects from whom the postmortem tissue samples derived raise the question of whether these Swedish adults, many with neuropsychiatric and addiction disorders (both of which are known to substantially reduce adult neurogenesis, as discussed by the authors), some institutionalized (neurogenesis is reduced in “deprived” conditions), and without any reason to think that they have lived adult lives with rich and diverse novel odorant stimulation, would be anywhere close to the limits of human OB adult-born neuron survival and incorporation into OB circuitry.